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Ping failed on mtu size over 6048 bytes

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  • 1.  Ping failed on mtu size over 6048 bytes

    Posted 07-12-2022 14:17
    Hi Eveyrone,

    I am facing a very strange where ping failed if size if over 6048 bytes

    {master:0}
    admin.paulin@core-wlt-01> ping rapid count 5 172.30.30.2 size 6048
    PING 172.30.30.2 (172.30.30.2): 6048 data bytes
    !!!!!
    --- 172.30.30.2 ping statistics ---
    5 packets transmitted, 5 packets received, 0% packet loss
    round-trip min/avg/max/stddev = 11.060/28.733/61.329/17.553 ms

    {master:0}
    admin.paulin@core-wlt-01> ping rapid count 5 172.30.30.2 size 6049
    PING 172.30.30.2 (172.30.30.2): 6049 data bytes
    .....
    --- 172.30.30.2 ping statistics ---
    5 packets transmitted, 0 packets received, 100% packet loss

    That happen in either direction. On both side the mtu is properly configured at L2 and L3 level

    root@core-krk-02> show interfaces xe-0/0/23:0 detail | match mtu
    Link-level type: Ethernet, MTU: 9014, LAN-PHY mode, Speed: 10Gbps, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, Source filtering: Disabled
    Protocol inet, MTU: 9000

    admin.paulin@core-wlt-01> show interfaces xe-1/0/47 detail | match mtu
    Link-level type: Ethernet, MTU: 9014, LAN-PHY mode, Speed: 10Gbps, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, Source filtering: Disabled
    Protocol inet, MTU: 9000


    What I have notice however, is that when I look at the traffic monitor, look like that traffic that goes out from QFX10002 (172.30.30.2) is seen only once, but when received on the other end, a QFX5110 (172.30.30.1) packets look to be duplicated (could it be due to the virtual chassis)

    Traffic monitor  from 172.30.30.2
    18:10:52.085073 Out IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 0, length 6057
    18:10:52.093393 In IP 172.30.30.1 > 172.30.30.2: ICMP echo reply, id 25901, seq 0, length 6057
    18:10:53.086302 Out IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 1, length 6057
    18:10:53.115041 In IP 172.30.30.1 > 172.30.30.2: ICMP echo reply, id 25901, seq 1, length 6057
    18:10:54.090315 Out IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 2, length 6057
    18:10:54.123462 In IP 172.30.30.1 > 172.30.30.2: ICMP echo reply, id 25901, seq 2, length 6057

    Traffic monitor from 172.30.30.1
    18:10:52.041650 In IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 0, length 6057
    18:10:52.041655 In IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 0, length 6057
    18:10:52.041673 Out IP 172.30.30.1 > 172.30.30.2: ICMP echo reply, id 25901, seq 0, length 6057
    18:10:53.042623 In IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 1, length 6057
    18:10:53.042631 In IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 1, length 6057
    18:10:53.042657 Out IP 172.30.30.1 > 172.30.30.2: ICMP echo reply, id 25901, seq 1, length 6057
    18:10:54.046674 In IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 2, length 6057
    18:10:54.046678 In IP 172.30.30.2 > 172.30.30.1: ICMP echo request, id 25901, seq 2, length 6057
    18:10:54.046695 Out IP 172.30.30.1 > 172.30.30.2: ICMP echo reply, id 25901, seq 2, length 6057

    Anyone has ideas/suggestion what else I could look at?


    ------------------------------
    Luc Paulin
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